Lance Richardson <lrich...@redhat.com> wrote:
> Some configurations (e.g. geneve interface with default
> MTU of 1500 over an ethernet interface with 1500 MTU) result
> in the transmission of packets that exceed the configured MTU.
> While this should be considered to be a "bad" configuration,
> it is still allowed and should not result in the sending
> of packets that exceed the configured MTU.
>
> Fix by dropping the assumption in ip_finish_output_gso() that
> locally originated gso packets will never need fragmentation.
> Basic testing using iperf (observing CPU usage and bandwidth)
> have shown no measurable performance impact for traffic not
> requiring fragmentation.
>
> Fixes: c7ba65d7b649 ("net: ip: push gso skb forwarding handling down the
> stack")
> Reported-by: Jan Tluka <jtl...@redhat.com>
> Signed-off-by: Lance Richardson <lrich...@redhat.com>
> ---
> net/ipv4/ip_output.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 03e7f73..4971401 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -239,11 +239,9 @@ static int ip_finish_output_gso(struct net *net, struct
> sock *sk,
> struct sk_buff *segs;
> int ret = 0;
>
> - /* common case: fragmentation of segments is not allowed,
> - * or seglen is <= mtu
> + /* common case: seglen is <= mtu
> */
> - if (((IPCB(skb)->flags & IPSKB_FRAG_SEGS) == 0) ||
> - skb_gso_validate_mtu(skb, mtu))
> + if (skb_gso_validate_mtu(skb, mtu))
IPSKB_FRAG_SEGS is now useless and should be removed.
